The bladder is a hollow, balloon-shaped organ in the pelvis. It is part of the urinary system. Urine made in the kidneys passes through the ureters to the bladder, where it is stored. The bladder has a flexible, muscular wall that allows it to expand (get larger) and contract (get smaller). When the bladder is full, the muscles tighten and urine is passed out of the body through the urethra.
The bladder wall is made up of 3 layers.
- The urothelium lines the inside of the bladder, ureters and urethra. It is made up of urothelial cells, or transitional cells. It is also called the transitional epithelium.
- The lamina propria is a layer of connective tissue. It separates the urothelium from the outer muscularis layer. It contains blood vessels, nerves and glands. The lamina propria is also called suburothelial connective tissue or subepithelial tissue.
- The muscularis is the outer layer of the bladder. It is made up of 3 layers of smooth muscle tissue (bladder muscle) called the inner longitudinal, middle circular and outer longitudinal muscles. The muscularis is also called muscularis propria.
Other layers of tissue separate the bladder from nearby organs.
- The serosa, or serous coat, is a thin membrane of connective tissue. It is only on the top part of the bladder.
- The adventitia is connective tissue that covers areas of the bladder where there is no serosa.
- The perivesical fat is a layer of fat that surrounds the bladder. It is outside the serosa and adventitia.
The bladder stores urine. Urine is made by the kidneys and travels to the bladder through 2 long tubes called ureters. When the bladder is full, the muscles in the bladder wall tighten to pass urine out of the body through the urethra.